1. Field of the Invention
The invention relates to the field of stripline circuitry, and more particularly to cross-over configurations that maintain isolation between two independent potentially intersecting striplines on a planar circuit.
2. Description of the Prior Art
Monolithic planar stripline circuitry at times requires two lines to cross paths. Since the striplines are independent, the crossing paths must be arranged in a manner that maintains electrical isolation between the striplines. One method for accomplishing such a cross-over in the prior art positions a second stripline layer beneath the first stripline layer and performs the cross-over on the second layer. If the phase relationship between the striplines is not a consideration, the cross-over can be accomplished by breaking one of the crossing striplines in the cross-over region and providing a transition from one section of the broken stripline to a secondary stripline on the second layer. The secondary stripline crosses the non-broken line on the second layer. A transition from the secondary stripline to the other section of the broken stripline completes the cross-over.
If the phase relationship between the striplines must be maintained, both striplines are broken in the cross-over region and coupled to secondary striplines on the second layer with transitions as previously discussed. These secondary striplines are arranged on the second layer to be non-contacting and to have equal line lengths, thus providing a cross-over which maintains the phase relationship between the crossing lines. Such a crossover consists of four gold plated pins, eight delicate free standing solder connections, four dielectric beads, at least four spacers, and thirty-two bolts with accompanying nuts, lock washers, and flat washers. The mechanical complexity of a two layer stripline circuit causes its fabrication to be extremely costly and the results in a structure that is large and heavy.
A technique in the prior art for realizing a stripline cross-over for a planar circuit, without using a second dielectric layer, breaks the crossing lines in the cross-over region and transfers each section of the broken lines to connectors positioned at an edge of the stripline structure. Cables are then utilized to couple the corresponding sections of the crossing striplines. This technique does not maintain the phase relationship between the crossing striplines as well as the secondary lines on a second dielectric substrate. Though the connector-cable approach provides poorer performance than the secondary line approach, it results in similar size, cost, and complexity.
Another cross-over method of the prior art does not break the two intersecting lines. This method is disclosed in U.S. Pat. No. 5,510,757 issued to Kumai et al, which is assigned to the assignee of the present invention. In this method the first line is deposited on the substrate and runs continuously through the cross-over region. A dielectric layer is deposited over the first line in the cross-over region and the second line is deposited on the substrate and over the dielectric layer. To provide a ground in the cross-over region holes are bored through the substrate to the ground plane and filed with electrical conducting material from the ground plane to the surface of the substrate. This type of cross-over, though relatively simple, establishes a stripline characteristic impedance in the crossover region that differs from the stripline characteristic impedance on substrate.